The Levites, however, were not numbered along with them by the tribe of their fathers.
47. But the Levites, after the tribe of their fathers We shall indeed hereafter see that they also were numbered, but Moses means that they were not included in the general census of the people, because God had chosen them to be His own property, and thus had severed them from the rest of the people.
Care is here taken to distinguish from the rest of the tribes the tribe of Levi, which, in the matter of the golden calf, had distinguished itself, Exo 32:26. Note, Singular services shall be recompensed with singular honours. Now, I.
Commenting on Numbers 1:47-54
But the Levites . . . were not numbered among them--They were obliged to keep a register of their own. They were consecrated to the priestly office, which in all countries has been exempted customarily, and in Israel by the express authority of God, from military service.